The invention relates to a screw comprising a shank provided with a thread at least on part of its length, and a head provided with a tool drive, wherein at least one shoulder disposed at an axial distance from a bearing face is formed on the head of the screw, and this shoulder extends in at least portions radially beyond a portion adjoining the shoulder on the shank side.
Extremely diverse requirements apply to screws with a head and a tool drive. In addition to an appropriately esthetic appearance specifically for use in a visible area in building construction or apparatus construction or in the automobile industry, the main considerations are secure retention and guidance of the screw while it is being driven in. Another common requirement is that appropriate safety precautions be taken to ensure that the screw cannot be easily loosened or completely detached by tools of any kind.
The object of the present invention provides a screw of the type cited in the introduction, which can be securely immobilized in axial direction in the region of the head and in which a tool therefore remains reliably engaged even if the axial length of a tool drive is short.
According to the invention, it is proposed for this purpose that a portion of the head adjoining the shoulder on the shank side is provided as a tool drive formed as an external drive.
By these features according to the invention, axially secure retention of the head of the screw in an appropriate tool is therefore possible in each case, since a shoulder disposed at a distance from the bearing face of the screw head is provided. Thereby the possibilities are created of using a tool which can engage on the underside of the screw head or the shoulder provided according to the invention, in such a way that this engagement can be maintained until the screw has been finally tightened. Accordingly, even after the screw has been finally tightened, the shoulder provided according to the invention is disposed at an axial distance from the bearing face of the head. Whether the tool drive is now disposed on the portion of the head disposed under the shoulder, on the shoulder itself or even in the region above the shoulder relative to the shank of the screw is of secondary importance. Since the head as seen in axial direction of the screw can be secured in an appropriate tool by the projecting shoulder, a special axial length of the tool drive is also not needed, since the tool itself also cannot be displaced axially relative to the screw. Until the screw has been finally driven in, therefore, or in other words has been finally set, the tool and screw form a kind of unit, since the screw can be firmly clamped in the region of the shoulder on the head, in such a way that engagement of the tool with a corresponding tool drive of the screw takes place simultaneously with clamping of the head.
Despite the shoulder, which can perhaps be regarded as an additional structural configuration of the head, it is possible to provide the screw with a head which is relatively low when viewed in and axial direction and which can be formed with an esthetic appearance. Since the possibility of a tool drive with short axial length exists in such a structure, such a screw also qualifies as a special safety screw, since loosening with other types of tools of any kind is not possible.
Precisely in a configuration in which the tool drive is formed on a portion of the head of the screw adjacent to the shank and in which the portion of the head remote from the shank of the screw is designed as a shoulder, and this shoulder extends radially beyond the portion of the head with the tool drive, there are achieved additional advantages with respect to head height and safety against unauthorized improper turning of the screw. By means of such an expedient, not only can the head be kept very low, but also the tool drive on the portion disposed under the shoulder has only a very short axial length, and so, after the screw has been finally set, a standard socket wrench can never be inserted under the shoulder for the purpose of being able to establish engagement with the portion equipped with the tool drive. In such a configuration, the esthetic appearance of the screw head merits particular mention, since only by very close scrutiny can it be seen that an engagable portion with a tool drive is present under the shoulder, which is always externally visible. In this way the shoulder can even form the uppermost termination of the head of the screw and thus be given a completely smooth configuration without tool drive.
In another alternative embodiment it is provided that a portion adjoining the shoulder on the shank side adjoins a disk-shaped part forming the bearing face of the head. Thus a head is formed which for practical purposes has, between two portions of larger diameter or of larger radial dimensions, an annular recess, which constitutes the portion adjoining the shoulder. Thereby the head has been provided with a larger face for bearing on the workpiece if such is needed, although in this case the shoulder disposed at a distance from the bearing face serves the purpose of being seized by an appropriate tool. The tool in turn can then engage with the underside of the shoulder from behind, since the portion of smaller diameter or smaller outside dimensions directly adjoins the shoulder.
In a further embodiment, an additional tool drive is formed on the side of the shoulder remote from the shank. This indeed provides easier accessibility for subsequent loosening of a screw that has been set, but even here a tool drive with relatively short axial length can be used and thereby correspondingly increased safety achieved once again. In tool drives of relatively short axial length, it is almost impossible to loosen a firmly tightened screw with any kind of socket wrench or open-ended wrench, unless exact and fixed alignment relative to the axis of the screw can be achieved.
In this connection, an axially protruding portion with an external tool drive can be formed on the side of the shoulder remote from the shank. The possibility therefore also exists of providing a corresponding internal tool drive directly at the upper side of the shoulder. Since it is possible in principle to form an internal tool drive with only short axial depth, additional safety precautions against loosening can also be built in here. In this connection, the possibilities are not limited merely to a hexagon socket or special internal drives with regular contours; instead, it is entirely possible to provide slots or ridges having very special shape, in order to permit exact matching to tools of the manufacturer in question.
Within the scope of the invention, it is also conceivable to provide, instead of a portion adjoining the shoulder in one piece on the side of the shank of the screw, a different alternative embodiment. For this purpose it is proposed that, in order to create an axial distance between the shoulder and the bearing face on a workpiece, a washer smaller in diameter than the shoulder be provided and be insertable noncaptively or captively under the shoulder. Thus it is not always necessary for a portion adjoining the shoulder in one piece to be present, but instead this axial distance can also be achieved precisely by a washer. In fact, to ensure that secure retention of the screw head can be maintained during the driving-in process until the screw has been finally set, it is merely necessary to create an appropriate axial distance under the shoulder. The tool, while actually holding the screw in appropriate manner in the region of the shoulder, should then not come into contact with the workpiece while tightening the screw underneath the shoulder.
In this connection, it is also possible to construct an additional disk-like part, which adjoins a corresponding portion under the shoulder, in one piece with the head of the screw or to form it as a washer.
As a rule, it will be sufficient if at least one of the portions of the head of the screw or just the shoulder on the head of the screw is provided with a tool drive. It is also conceivable, however, for a plurality of portions of the head disposed successively and if appropriate spaced apart in the axial direction of the screw to be provided with a tool drive. In this connection it is possible for these multiple portions also to have the most diverse forms of tool drives.
Precisely for forming a plane terminating face on the head of the screw and thus for giving the optical impression of appropriate safety against being loosened by turning, it is advantageous for the shoulder viewed in axial direction of the screw completely to mask the shank-side portion containing the tool drive, so that the tool drive is disposed completely underneath and inside the outside boundary of the head.
In a further proposal, the shoulder and one or more additional, disk-like parts have the same or different size and/or outside contour. Thereby not only are different practical alternatives of such a screw conceivable, but also there are also derived therefrom the most diverse combinations of tool drives, which cannot be engaged with a standard tool. By virtue of the expedients of the invention, therefore, the most diverse alternative forms of screw heads are conceivable, in which, however, it must always be guaranteed that the screw is axially secured throughout the entire driving-in process and thus also held in axially aligned condition, and that the tool drive remains constantly inserted in exactly aligned orientation with the tool during the driving-in process.
In one very simple alternative, an external tool drive is formed on the shoulder itself. However, the safety features for an external drive on the shoulder itself must meet much stricter requirements than when a tool drive is disposed on the portion provided under the shoulder.
Several options are possible for the tool drive, the simplest alternative being that in which the tool drive has a polygonal or noncircular cross section. In this connection, it would also be conceivable that, for a self-forming thread on the shank and a corresponding trilobular cross section of the shank, for example, the tool drive also has trilobular form at the corresponding portion. In the scope of the invention it is also conceivable that a tool drive in the form of recesses and/or raised structures and/or symmetric or asymmetric peripheral contour will be provided.
By means of the expedients according to the invention, the head shape of a screw can be configured very individually, while nevertheless assuring appropriate retention during the actual driving-in process. Thus it is possible for the shoulder to have cylindrical, frustoconical or spherical-sector form. In this connection, it is advantageous for transitions or edges, especially those provided on the exposed end region of the head, to be rounded. The functions of engineering design and of esthetic surface can therefore be optimally coordinated.
In order to achieve safety against loosening of the screw in a very special way, it is proposed that the portion provided with the tool drive have axial length equal to or shorter than the shoulder forming part of the head. For the portion equipped with the tool drive, therefore, only a short axial length is necessary, and so the undercut remaining under the shoulder after final setting of the screw is hardly perceptible and already cannot be reached at all with a commercial tool.
Within the scope of the invention, however, it is also possible that the portion provided with the tool drive has an axial length the same or longer than the shoulder forming part of the head. Such aversion is applicable, particularly for aesthetic reasons for various cases in which a higher head is desired.
In a special configuration of the screw, it is provided that a boring part is formed on, attached to or inserted in the end of the shank remote from the head. Precisely because of the special configuration of the head and the possibility of retention and exact axial alignment, the features are usable even in self-boring and self-thread-cutting screws. Although only a short axial length is available for the tool drive, the torque necessary for a boring or thread-forming process can be transmitted without problems of any kind.